The present invention relates to a multi-layered sintered material which is suitable for sliding-contact members, washers and the like used in motor vehicles, industrial machines and agricultural machines, and which is excellent in corrosion resistance and wear resistance, and improved in wear resistance in a boundary lubrication state under severe lubrication conditions, and to a method of manufacturing the same.
Conventional multi-layered sintered materials for the above-mentioned bushes, washers and the like are mainly bronze or lead bronze. Those alloys have favorable sliding performances when they are used in a condition where lubricating oil exists. In a boundary lubrication state under severe conditions, however, wear resistance of the foregoing alloys is inferior, and an adequate sliding property can not be obtained. According to the previous suggestion from the engineers of DAIDO METAL Co., Ltd. including the present inventors, the wear resistance and also the lubrication performance can be improved by adding Ni-B compound, which are hard compounds, and graphite to the conventional bronze and lead bronze alloys (see JP-A-4-198440).
Recently, in order to reduce the friction loss, lubricating oil containing sulfur has been used. When a material is used in such a highly corrosive lubrication environment, sulfur corrosion of the copper alloy matrix occurs and affects the sliding property unfavorably, which results in a demand for producing materials which have corrosion resistance as well.